For a conventional image display unit such as a cathode-ray tube (CRT) or a field emission display (FED), a metal back-attached phosphor screen, which has a metal film formed on the inner surface (surface opposite to the face plate) of a phosphor layer, has been used extensively.
Such a metal film is called a metal back layer and aimed to enhance brightness by reflecting light, which is in light emitted from the phosphor material by electrons emitted from an electronic source and advances toward the electronic source, to the face plate side and to play a role as an anode electrode by giving the phosphor layer with conductivity. It also has a function to prevent the phosphor layer from being damaged by ions generated when gas remaining in a vacuum envelope is ionized.
However, the FED had a disadvantage that an electric discharge (vacuum arc discharge) was caused easily when an image is formed for a long period because a gap (space) between a face plate having a phosphor screen and a rear plate having an electron emission element was narrow to approximately one to several millimeters and a high voltage of about 10 kV was applied to the very narrow gap to form a high electric field.
And, when such an abnormal electric discharge occurred, a large discharge current of several to several hundred amperes flowed instantaneously, so that there was a possibility that the electron emission elements of a cathode section or the phosphor layer of an anode section might be destructed or damaged.
The present invention has been made to remedy the above-mentioned disadvantages and provides an image display unit which has high brightness and a high withstand voltage characteristic and can provide high quality display by suppressing a peak value of discharge current even if an electric discharge occurs, so to prevent the electron emission element or the phosphor screen from being destructed or deteriorated.